Phenobarbital

Uses	Treatment and management of Epilepsy/seizures
Therapy	Anti-Epileptic
Side Effects	Drowsiness, depression, fatigue, nausea, vomiting, hypotension, confusion, anaemia, constipation, slow heartbeat, double vision, staggering walk, fainting, suicidal thoughts

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Molecule Description

Phenobarbital is used to treat epilepsy (seizures). It slows down brain activity due to its hypnotic properties and thus helps in reducing the incidences of seizure attacks in patients who have epilepsy. Phenobarbital is also known as phenobarbitone. It belongs to a group of medicines called barbiturates.

Uses

Epilepsy or seizures (abnormal electrical activity in the brain)

Contraindications

When should one not use Phenobarbital

Allergic to Phenobarbital or any of the ingredients of this medicine.
Severe respiratory depression or have a history of respiratory diseases like chronic obstructive pulmonary disease (COPD).
Severe kidney or liver failure
Planning for pregnancy or are already pregnant
Acute intermittent porphyria

Side effects

Common side effects of this drug are:

Drowsiness
Depression
Memory impairment
Low blood pressure
Respiratory depression
Altered blood cell counts: agranulocytosis, thrombocytopenia
Megaloblastic anaemia (due to folate deficiency)

Precautions and Warnings

Pregnancy

No, Phenobarbital is unsafe during pregnancy. Studies show a definite risk to the developing unborn baby. Since this medicine can cross the placenta, your baby can risk withdrawal symptoms if you take the medicine in the last few months of the pregnancy. Consult your doctor for evaluating the risks and benefits of your condition. Don't take it without consulting your doctor. Inform or consult your doctor at the earliest if you become pregnant while on treatment with Phenobarbital.

Breast Feeding

No, do not take Phenobarbital while breastfeeding without consulting your doctor. It has a low to moderate transfer to breast milk. It may cause unwanted side effects. Consult your doctor immediately if your baby shows signs of increased drowsiness, decreased activity, breathing problems or difficulty in breastfeeding.

Driving

If you experience any impairment in your vision while on treatment with Phenobarbital, it is advised to avoid driving. Phenobarbital can cause disorientation, drowsiness and dizziness, affecting your ability to drive.

Alcohol

No, it is not advised to take alcohol with Phenobarbital. Consumption of alcohol can lead to increased drowsiness, difficulty concentrating and increased risk of falling.

Other General Warnings

Talk to your doctor if

You have suicidal thoughts after taking Phenobarbital.
You experience any changes in blood cell counts.
You have decreased liver function.
You are suffering from kidney disease.
You're an elderly patient, the dose of Phenobarbital should be carefully monitored.
You're breastfeeding, pregnant or planning to conceive.
Your symptoms don't resolve or clinical worsening of the condition.
You see any skin reaction, as this medicine can cause serious skin conditions like toxic epidermal necrolysis and Steven-johnson syndrome (life-threatening skin conditions).
You want to discontinue this medicine. Don't abruptly stop taking this medicine as it may cause withdrawal symptoms.
You are using oral contraceptives.

Mode of Action

How Does It Work?

Phenobarbital increases the activity of gamma-Aminobutyric acid (GABA) receptors in the brain. GABA is a chemical messenger in the brain that reduces and controls the nerve cells' excess and abnormal electrical activity.

Interactions

Interactions with other medicines

Monoamine oxidase inhibitors (MAOIs) like Selegiline - decrease the antiepileptic activity of Phenobarbital.
Selective serotonin reuptake inhibitors (SSRIs) like Citalopram decrease the antiepileptic activity of Phenobarbital by lowering the convulsive threshold.
Interaction with Valproate- can increase the serum concentration of Phenobarbital by decreasing its hepatic metabolism.
Interaction with other antiepileptic medicines like Phenytoin, Carbamazepine, and Oxcarbazepine can increase the hepatic metabolism and lower the serum concentration of Phenobarbital.
St John's wort (Hypericum perforatum) – the antiepileptic activity of Phenobarbital is reduced by concomitant use of the herbal remedy St John's wort.
Folic acid - if folic acid supplements are given to treat folate deficiency, blood levels of Phenobarbital may decrease, leading to decreased seizure control in some patients.
Anti-arrhythmics like Disopyramide and Quinidine - decrease in the anti-arrhythmic activity of these medicines. Changes in dosage may be necessary.
Antibacterials like chloramphenicol, doxycycline - Phenobarbital reduces the blood levels of these medicines leading to decreased antibacterial activity.
Aripiprazole and other antipsychotics - Phenobarbital reduced blood levels of these medicines.

Interactions with food items

After oral administration, absorption of Phenobarbital is not affected by food. No interaction with food has been found.

Dosage

Overdose

Symptoms of a Phenobarbital overdose include: blurred or double vision, drowsiness, dysarthria, ataxia, nystagmus (rapid side-to-side movement of eyes), tiredness, fainting, confusion, dizziness, nausea, rash, shock (extremely low blood pressure), slowed or absent breathing, low blood pressure, decreased level of alertness (stupor), slurred speech and coma. The duration and depth of signs of cerebral depression vary with the patient's dose and tolerance.

Missed a Dose

If you have missed a dose of Phenobarbital, take the dose as soon as possible. However, if the time lapse is long and you are approaching the next dose, skip the missed dose and continue the regular dosing schedule. Do not take a double dose for making up the missed dose. You can reach out to your doctor for further instructions.

Frequently Asked Questions (FAQs)

Phenobarbital should be used with caution in elderly patients because they are more prone to other medical problems like hepatic and renal impairment. Dose adjustment needs to be done based on their condition. Some common side effects like sleepiness or unsteadiness may increase the risk of pre-existing conditions.

It may take up to 60 minutes for you to notice this medicine's effects. Phenobarbital's effects can last up to 10 to 12 hours. It varies from person to person and the dosage of the medicine. Don't change the dose. Consult your doctor if you don't see any results of the medication.

Yes, Phenobarbital is a habit-forming medicine. It can cause addictive behaviour if used for the long term. Therefore the dose must be carefully monitored.

No, Phenobarbital should not be taken without a doctor's prescription.

Clinical studies have shown that Phenobarbital can cause learning impairments, behavioural and learning problems. It can worsen the condition by increasing existing hyperactivity and aggressive tendencies. Consult your doctor immediately if you notice any such side effects.

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